(1) Field of the Invention
The present invention generally relates to transmission devices, and more particularly, to a transmission device that performs signal regeneration control.
(2) Description of the Related Art
Multimedia times including the Internet have come and the optical communication network technology in a core communication system has been desired to provide much more advancement and broadening of services. And development is progressing quickly towards the information society.
The channel capacity of optical communication is changing from mainstream 2.4 Gb/s to 10 Gb/s. The receiving part in the optical transmission system has been required to have much more advanced receiving functions with increased channel capacity and higher bit rate.
The light receiving part has a fundamental operation such that a received light signal is converted into an electric signal by a photodiode, waveform shaping and noise band restriction being imposed thereon by means of an equalizing filter. Then, a clock timing is extracted by a timing extracting part. A “1”/“0” decision is made by a decision making part in synchronism with the extracted synchronizing clock, so that data can finally be retrieved. In the light receiving part, the above-mentioned regeneration control is performed so that the received light signal that has been attenuated and contained noise is regenerated so as to have an error rate equal to or lower than the target error rate.
The conventional light receiving part widely employs a SAW (Surface Acoustic Wave) filter arranged in the timing extracting part in order to extract the particular clock timing from the input signal. Therefore, there is a disadvantage in that the conventional light receiving parts are capable of handling only single transmission rate and the transmission devices are not flexible.
Regarding optical fiber transmission, different optical fibers have different refractive indexes, and optical transmission paths slightly vary with different wavelengths. This results in differences in the propagation time of light for the same optical fiber. This phenomenon is called waveform dispersion, which is a factor restricting the optical transmission quality.
The conventional light receiving part measures a waveform distortion because of wavelength dispersion, and the optimal point in the decision making part is manually determined for each device. In the setting of the optimal point, it is required to consider difference in the practical devices caused during production, and variations in temperature and/or power supply voltage. Thus, the conventional transmission devices are not efficient, convenient, and reliable.